Merged Causes

A case where two defendants separately breach duties owned to a plaintiff, but there is an issue proving but-for causation in that each defendant can use the defense that neither of their breaches were there but-for causation of the plaintiff's harm, since the plaintiff would have been harmed even if one defendant did not breach his or her duty to the plaintiff.

In dealing with cases of this nature, the court uses the "substantial factor test," which when there is a merged causes situation, the court asks if each individual breach was itself a substantial factor, meaning that it could have caused the harm individually, even though it did not. If a defendant's breach is deemed a substantial factor, the defendant is held liable. Using this test, multiple defendants can be held jointly and severally liable for breaching a duty towards a plaintiff.